Retinitis pigmentosa (RP) refers a group of hereditary retinal degenerations that are the most frequent genetic cause of blindness in adulthood. The disease is characterized not only by the progressive loss of peripheral rod and cone function but also by dysfunction of the foveal cone system. This research proposal is focused on deficits in foveal contrast perception in patients with RP. The ability to perceive variations in contrast is crucial to an accurate perception of the visual environment, and deficits in contrast perception can have an adverse impact on the quality of life for RP patients. The proposed studies are designed to establish the underlying mechanisms of foveal contrast processing abnormalities in RP patients and determine the impact of these abnormalities on patients' visual function. Parallel investigations of normal control subjects will better define mechanisms of contrast processing in visually normal individuals. The specific aims are: (1) to define the contribution of spatial sampling abnormalities to the foveal visual acuity loss of patients with RP; (2) to determine the relationship between deficits in spatial contrast sensitivity, temporal contrast sensitivity, and motion perception in patients with RP in order to establish the extent to which abnormal early temporal filtering contributes to patients' contrast sensitivity loss; and (3) to characterize the relationship between contrast sensitivity and deficits in suprathreshold contrast processing in RP patients in order to determine the impact of photoreceptor disease on postreceptoral contrast processing mechanisms. These aims will be accomplished by a series of interrelated psychophysical investigations of foveal visual dysfunction in subjects recruited from a cohort of approximately 1,000 well- categorized patients with RP, many with identified mutations in the genes involved in rod phototransduction, available through the University of Illinois Research Center of The Foundation Fighting Blindness. These studies are intended to lead to a better understanding of the relationship between foveal vision loss and underlying disease pathophysiology in RP, to clinically applicable methods that will allow an earlier detection and a more precise characterization of foveal visual impairment in individual patients, to the optimization of strategies for clinical management and visual rehabilitation, and to the more sensitive evaluation of potential methods for therapeutic intervention.